1. Field of the Invention
This invention relates to formulations of nerve growth factor ("NGF") and their use to induce nerve cell growth, differentiation, survival, repair, maturation, or function in vitro, in vivo or ex vivo. More particularly, this invention relates to microencapsulation compositions having controlled release characteristics, preferably with increased stability, for the NGF component, particularly human recombinant NGF ("rhNGF"). Methods for making and using such compositions are provided.
2. Description of Related Disclosures
Nerve growth factor (NGF) is a neurotrophic factor required for the growth and survival of sympathetic and sensory neurons during development and in mature animals (Thoenen, et al., Physiol. Rev. 60:1284-1335 (1980)). Clinical indications for recombinant human NGF include peripheral sensory neuropathy and Alzheimer's disease. For example, the systemic administration of NGF has been shown to reduce the sensory neuropathy induced by administration of cisplatin and taxol to mice (Apfel, et al., Ann. Neurol. 29:87-90 (1991); Apfel, et al., Ann. Neurol. 31:76-80 (1992)). In recent clinical trials, NGF has been administered to humans to improve sensory function in diabetic neuropathies (Petty, et al., Ann. Neurol. 36:244-246 (1994)). Although non-toxic and efficacious, administration of NGF in liquid parenteral formulation has been reported as associated with injection-site hyperalgesia and, particularly, myalgesia in current clinical trials.
Intracerebroventricular (ICV) administration of rhNGF can prevent degeneration of basal forebrain cholinergic neurons in rats and monkeys with fimbria-fornex lesions (Koliatsos, et al., Exp. Neurol. 112:161-73 (1991); Koliatsos, et al. Ann. Neurol. 30:831-40 (19991); Tuszynski, et al. Ann. Neurol. 30:626-36 (1991)). Studies have shown that ICV administration of rhNGF can enhance choline acetyltransferase activity and improve spatial memory in aging rats (Williams, Neurobiol. Aging 12:39-46 (1991); Fischer, et al., J. Neurosci. 11(7):1889-1906 (1991)). The ICV delivery of rhNGF across the blood-brain barrier has been accomplished by syringe, Ommaya.RTM. reservoir or Alzet pump. For the treatment of Alzheimer's disease, the use of implantable infusion pumps with catheters to deliver rhNGF continuously and directly to the ventricle of the brain has been considered. However, rhNGF has been observed to degrade via deamidation and iso-aspartate formation in some implantable pumps at 37.degree. C. (physiological condition), as determined by RP-HPLC. The stability of NGF, particularly in liquid, is complicated beyond the usual chemical and physical degradation pathways as a result of the dimeric structure of NGF. Protein stability may be further complicated when recombinant protein is a mixture of C-terminally clipped NGF variants. While NGF normally exists as a dimer (the crystal structure of murine NGF shows 3 antiparallel pairs of b-strands forming a flat surface through which the monomers dimerize (McDonald, et al. Nature 354:411-414 (1991)); the dimer dissociation constant is.ltoreq.10.sup.-13 M (Bothwell et al., J. Biol. Chem. 252:8532-8536 (1977); Timm, et al., Biochem. 33:4667-4676 (1994)), higher order aggregation of NGF has been observed.
Thus, there exists a need for formulations containing NGF that maintain NGF stability and activity while providing a means for treating a variety of conditions, being effective for therapeutic administration to mammals, particularly human subjects, and particularly for intracerebral administration. The advantages of the present invention meet these needs and others as well.